2. In large bowl, with mixer on medium speed, beat sugar, vanilla, salt and remaining 6 tablespoons butter 2 to 3 minutes or until light and creamy. Beat in eggs 1 at a time until incorporated. With mixer on low speed, beat in chocolate mixture; beat in flour and sour cream. Pour batter into prepared baking dish; sprinkle remaining 1/2 cup chocolate chips and walnuts evenly over batter.